1. Field of the Invention
The present invention relates to a stop control system for an internal combustion engine, which automatically stops and restarts the engine installed on a vehicle.
2. Description of the Related Art
Conventionally, as a stop control system for an internal combustion engine of this kind, one disclosed in Japanese Patent No. 4475437 is known. The engine is automatically stopped during stoppage of a vehicle when predetermined stop conditions (idle stop conditions) are satisfied. Further, the engine is connected to a compressor of an air conditioner via a crankshaft, and is used as a drive source of the compressor. This can cause the following inconveniences when the engine is stopped during a cooling operation of the air conditioner.
After stoppage of the engine, although the blowing of air into a vehicle compartment by an electric fan is continued, the circulation of refrigerant is stopped along with stoppage of the compressor, whereby the temperature of an evaporator starts to rise. Since air having passed through the evaporator is blown out into the vehicle compartment, the temperature of the air progressively rises as the temperature of the evaporator rises. Further, when the engine is stopped, dehumidification ceases to be performed, and humidity in the vehicle compartment starts to rise. When the humidity in the vehicle compartment becomes equal to or higher than a predetermined value, fogging of the window glass of the vehicle compartment occurs.
Therefore, in the stop control system disclosed in Japanese Patent No. 4475437, after the engine is automatically stopped, when a predetermined engine stoppage time period has elapsed, the engine is restarted. The engine stoppage time period is set in the following manner: First, an upper limit temperature (allowable upper limit temperature) of the evaporator of the air conditioner below which it is possible to maintain the comfort of vehicle occupants in the vehicle compartment is calculated according to the settings of the air conditioner and the external environment. Then, a time period (compartment temperature rise allowable time) over which the comfort of vehicle occupants in the vehicle compartment can be maintained is calculated based on the difference between the calculated allowable upper limit temperature and the temperature of the evaporator detected immediately before the stoppage of the engine. Next, a limit of humidity (fogging-determining humidity) below which fogging of window glass does not occur is calculated according to the settings of the air conditioner, temperature in the vehicle compartment, and the external environment, and fogging occurrence estimated time which is estimated to take before fogging of the window glass occurs is calculated based on the difference between the calculated fogging-determining humidity and humidity in the vehicle compartment detected immediately before the stoppage of the engine. Then, a smaller one of the calculated compartment temperature rise allowable time and fogging occurrence estimated time is set as the engine stoppage time period. Next, when the set engine stoppage time period has elapsed after the automatic stopping of the engine, the engine is restarted to thereby prevent both degradation of the comfort of vehicle occupants in the vehicle compartment and occurrence of fogging of the window glass.
As described above, in the stop control system disclosed in Japanese Patent No. 4475437, the fogging occurrence estimated time is calculated according to the settings of the air conditioner and the external environment, and the engine is restarted before the fogging occurrence estimated time has elapsed. However, conditions of occurrence of fogging of the window glass are not determined by the above-described parameters alone but vary with the temperature of the window glass where fogging actually occurs. Further, even if the temperature of the window glass at given time is the same, conditions of occurrence of fogging of the window glass are also different according to the environment in which the window glass has been placed up to the time.
However, in the conventional stop control system described above, the calculation of the fogging occurrence estimated time is merely performed according to the settings of the air conditioner and the external environment, which makes it impossible to accurately calculate the fogging occurrence estimated time. Therefore, when the fogging occurrence estimated time is calculated to be longer than actual fogging occurrence time, the restart of the engine is delayed to allow fogging of the window glass to occur. Inversely, when the fogging occurrence estimated time is calculated to be shorter, the engine is restarted quickly in a state where there is no fear of occurrence of fogging of the window glass, which degrades fuel economy.